The inventive concept is related to methods of forming a material layer during the fabrication of a semiconductor device. More particularly, the inventive concept relates to methods of forming a composition layer having a uniform composition ratio of constituent materials across the thickness of the layer.
The development of contemporary semiconductor devices is one characterized by ever higher degress of integration density and ever increasing operating speeds. These coincident demands for greater integration and operating speed create great pressure to improve the fabrication technologies enabling manufacture of semiconductor devices.
For example, as semiconductor devices become more highly integrated, the size of cell regions within the semiconductor devices are reduced. Accordingly, it has become increasingly difficult to form a capacitor providing sufficient capacitance for reliable operation of the semiconductor device. The capacitance “C” of the capacitor is directly proportional to the dielectric constant “∈” of its dielectric layer and the capacitive surface area “A” of its electrodes. The capacitance “C” of the capacitor is also inversely proportional to the distance “d” separating the electrodes. Thus the capacitance “C” of the capacitor may be expressed by the equation: C=∈A/d
For capacitors formed using a conventional dielectric material such as silicon oxide or silicon nitride, methods of forming cylindrical-shaped or fin-type lower electrodes have been developed to increase the effective area A of the capacitor, thereby increasing the capacitance C. However, the fabrication of highly complex electrode geometries is difficult and costly.
Accordingly, certain dielectric layers within semiconductor devices, such as gate insulation layers, capacitor dielectric layers, etc., are now formed using materials having a significantly higher dielectric constant than those provided by silicon oxide and silicon nitride. In one example, contemporary dielectric layers include those formed from a plurality of metal oxides, such as hafnium silicate, zirconium silicate, strontium titanium oxide, etc. This type of layer exhibits a much higher dielectric constant than silicon oxide or silicon oxynitride.
A dielectric layer formed from a plurality of metal oxides may be formed using conventionally understood chemical vapor deposition (CVD) process(es) and/or atomic layer deposition (ALD) process(es).
When a dielectric layer is formed using a CVD process or ALD process, a plurality of preliminary layers are typically formed and then heat treated to form the desired dielectric layer. Unfortunately, this approach to the formation of a dielectric layer yields a layer having a lower portion with a substantially different composition ratio than an upper portion. In other words, the thickness of the dielectric layer exhibits a non-uniform composition ratio.
Additionally, when a plurality of precursors are used in the formation of a dielectric layer, the composition ratio of constituent materials forming the layer is a function of the flow rate of the precursors. Thus, if the flow rate for a particular precursor is less than about 10% of the total flow rate of for all of the precursors, the resulting dielectric layer may include greater than about 10%, by atomic composition, of the precursor's primary elemental component (or “central atom”).